How to prevent adding same product to cart more than one time?

Question

As title says, how can I prevent adding same product to cart more than one time in Magento 2.4.2?

Answer 1

This plugin will work for simple and configurable products. You can throw an error or redirect e.g. to cart if product already exists in cart.

di.xml

<type name="Magento\Checkout\Model\Cart">
    <plugin disabled="false" name="Vendor_Module_Plugin_Magento_Checkout_Cart_BeforeAddToCart" type="Vendor\Module\Plugin\Magento\Checkout\Cart\BeforeAddToCart"/>
</type>

vendor/module/Plugin/Magento/Checkout/Cart/BeforeAddToCart.php

    <?php
    declare(strict_types=1);
    
    namespace Vendor\Module\Plugin\Magento\Checkout\Cart;
use Magento\Checkout\Model\Cart;
use Magento\Checkout\Model\Session;
use Magento\Catalog\Model\Product;
use Magento\Checkout\Model\Session\Proxy as SessionProxy;
use Magento\Framework\Message\ManagerInterface;
use Magento\ConfigurableProduct\Model\Product\Type\Configurable;
use Magento\Framework\UrlInterface;

class BeforeAddToCart {

    private $messageManager;
    private $cartSession;
    private $configurableProduct;
    private $url;
    private $session;

    public function __construct(
        Configurable $configurableProduct,
        ManagerInterface $messageManager,
        SessionProxy $cartSession,
        UrlInterface $url,
        Session $session
    ) {
        $this->messageManager = $messageManager;
        $this->cartSession = $cartSession;
        $this->configurableProduct = $configurableProduct;
        $this->url = $url;
        $this->session = $session;
    }

    public function beforeAddProduct(Cart $subject, $productInfo, $requestInfo=null)
    {
        $enableProductCartControl=true;

        $product = null;
        $parentProduct=null;

        if ($productInfo instanceof Product) {

            $product = $productInfo;
            if (!$product->getId()) {
                throw new \Magento\Framework\Exception\LocalizedException(
                    __("This product wasn't found. Verify the product and try again.")
                );
            }

        }

        if ($product)
        {
            // default product is simple
            //
            if ($product->getTypeId()==='configurable')
            {
                if (isset($requestInfo['super_attribute']))
                {
                    $parentProduct=$product;
                    $childProduct = $this->configurableProduct->getProductByAttributes($requestInfo['super_attribute'] ,$product);
                    // change $product to child
                    $product=$childProduct;
                }
            }

                if ($product && $enableProductCartControl)
                {
                    // check for existence of product in cart...
                    if($this->cartSession->getQuote()->hasProductId($product->getId())){

                        // redirect to cart
                        $this->session->setRedirectUrl($this->url->getUrl('checkout/cart/index'));
                        throw new \Magento\Framework\Exception\LocalizedException(
                            __("[x] This product is already in the cart. Testing, testing : ". $product->getSku())
                        );
                    }

                }


        }

        return [$productInfo, $requestInfo];

    }

    /**
     * Get request for product add to cart procedure
     *
     * @param \Magento\Framework\DataObject|int|array $requestInfo
     * @return \Magento\Framework\DataObject
     * @throws \Magento\Framework\Exception\LocalizedException
     */
    private function _getProductRequest($requestInfo)
    {
        if ($requestInfo instanceof \Magento\Framework\DataObject) {
            $request = $requestInfo;
        } elseif (is_numeric($requestInfo)) {
            $request = new \Magento\Framework\DataObject(['qty' => $requestInfo]);
        } elseif (is_array($requestInfo)) {
            $request = new \Magento\Framework\DataObject($requestInfo);
        } else {
            throw new \Magento\Framework\Exception\LocalizedException(
                __('We found an invalid request for adding product to quote.')
            );
        }
        return $request;
    }
}

Answer 2

You can use plugin for that

in you di.xml

<type name="Magento\Checkout\Model\Cart">
<plugin name="prevent_add_to" type="vendor\Module\Plugin\Beforeaddtocart"/>
</type>

vendor\Module\Plugin\Beforeaddtocart.php

<?php

namespace vendor\Module\Plugin;

class Beforeaddtocart{
    
    public function beforeAddProduct(\Magento\Checkout\Model\Cart $subject, $productInfo, $requestInfo=null){
        $objectManager = \Magento\Framework\App\ObjectManager::getInstance();
        $session = $objectManager->create('\Magento\Checkout\Model\Session');
        
        $product_id = $requestInfo['product'];
        $quote = $session->getQuote()->hasProductId($product_id);
        if($quote){
            throw new \Magento\Framework\Exception\LocalizedException(
                    __("The product is already in cart you can't add more than 1 qty")
                );
        }
        return [$productInfo, $requestInfo];

    }
}

note: Please don't use objectmanager directly